The present invention relates generally to the field of rotary cutter heads used for woodworking machinery and in particular, to a novel rotary cutter head shape and knife anchorage system which shifts the mass of the cutter head to a more useful location at the base of the knife blades while removing cutter head mass from forward of the cutting surface of the knife blade and which provides reproducible height registration of the knife within the cutter head.
Typical of the majority of cutting heads is the use of two or more knife blades in a cutter head to distribute the cutting activity fully around the rotating cutter head. This reliance on anywhere from two to twelve knife blades is intended to reduce the strain on each individual knife while also reducing the amount of bite each blade must take from the wood and thereby providing a smoother cut on the wood and to even out the operation of the cutting head by distributing the points of impact against the workpiece fully around the diameter of the cutter head.
One drawback of this type of cutter head construction is that as the number of blades in a cutter head increases, the amount of area available to support each blade is reduced and the space for the mechanism used to secure the blade is reduced commensurately. This results in each blade being less securely locked into the cutter head and increases the possibility that a blade will loosen during use. A loose blade can ruin the workpiece and cause increased down time while the head is shut down, the loose blade retightened and its height readjusted to be uniform to the other blades installed in the cutter head. It will be appreciated by those skilled in the art that as the number of blades increases, so does the opportunity for any one blade to become loose or improperly aligned, therefore, either destroying the workpiece or causing additional downtime while adjustments are made to the cutter head. For many years blades have been held in cutter heads using combinations of set screws, knife receiving recesses in the cutter block, wedge means and spring pressure means to secure the knife blades in the cutter head, and to resist centrifugal force on the knife blade which tends to force the blades away from the cutter head. Depending on the configuration of these devices it is frequently necessary to shift the cutter head to several different positions in order to release or secure a knife with respect to the cutter head. In other cutter head configurations, it may be required to have access to the side of the cutter head to remove or install a knife. This shifting of the cutter head or side access requirement can make knife removal or installation a difficult and time consuming procedure and permit the position of the knife to change during installation procedures. This leads to knives which are not at equal height which causes a wavy cut on the work piece which is unacceptable.
It will further be appreciated by those skilled in the art that as the number of knife blades on a cutter head increases, so does the time increase which must be devoted to adjustment of the cutter head blades. It must be ensured that the blades are reasonably uniform in terms of their knife-edge profile, their mass, and their length so that the blades do not unbalance the cutter head once installed and prevent useful operation of the cutter head. An examination of the prior art reveals that a variety of adjustment means have been utilized to allow the individual knife blades to strike the workpiece at a uniform height above the center of the cutter head. As previously noted, if the blades are not uniform in height, a wave or ripple effect is caused in the workpiece, leaving the workpiece unusable or, alternatively, increasing the amount of finish time which must be devoted to the workpiece to make it suitable for use. However, generally these knife adjustment means incorporated into prior art devices allow minor changes in knife-height to be made by an operator installing a knife. These same adjustment means also permit the knives to be mis-adjusted and differently adjusted. This ability to adjust knife position, while helpful on the one hand, can be the source of problems on the other hand since the knife can be mis-adjusted as well as correctly adjusted.
Therefore, as the number of knife blades increases on any cutter head, the amount of time and effort and care which must be devoted to ensuring that each additionally installed knife blade is the equal to the previously installed knife blades increases, and the opportunity for failure for any one knife blade commensurately increases.
Various solutions to these problems have been attempted in the prior art, but none with complete satisfaction. The present invention provides a solution to these problems by providing a cutter head which allows knife insertion and removal while the cutter head is held in a single position. In this single position the knife securing means can be released and tightened while the knife is held in its proper position. In addition, the inventive cutter head and knife combination provides positive knife height registration of the knife with respect to the cutter head while avoiding the previous causes of any knife-shifting movements during tightening procedures. The present invention also permits sets of knives to be made which are of identical height, length, weight and shape which then can be inserted into the cutter head with reproducible and identical positioning of each knife. This attribute of the invention permits simplified cutter head balancing and dependable and reproducible knife height positioning of the set of knives in the cutter head. This accurate knife height positioning avoids a wavy cut in the workpiece which occurs when the knives in a cutter head are at different heights and therefore producing a different depth of cut in the workpiece.